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Design and Nuclear-Safety Related Simulations of Bare-Pellet Test Irradiations for the Production of Pu-238 in the High Flux Isotope Reactor Using COMSOL

The Oak Ridge National Laboratory (ORNL) is developing technology to re-establish the capability to produce plutonium-238 for the National Aeronautics and Space Administration (NASA) as a power source material for powering vehicles while in deep-space. The High Flux Isotope Reactor (HFIR) of ORNL has been utilized to perform test irradiations of in-capsulated neptunium oxide (NpO2) and aluminum powder bare pellets for purposes of understanding the performance of the pellets during irradiation. Post irradiation examinations (PIE) are currently underway to assess the effect of temperature, thermal expansion, swelling due to gas production, fission products, and other phenomena.

In order to properly design and assess the nuclear-safety implications of the NpO2 pellets used to produce Pu-238, COMSOL v4.2a has recently been qualified to perform nuclear-safety-related calculations at HFIR. The present design and safety analysis simulates the bare-pellet test capsule assembly in full three dimensions (3D) over a quarter slice of the capsule.